Hi
you should consider implementing an approximation of the function via
polynomial evaluation. This involves the computation of
fixed-/floating-point coefficients for the polynomial either the Taylor
or the Remez (minimax) way.
One good source for approximations of transcendental functions is
fdlibm:
http://www.netlib.org/fdlibm
Best regards
Nikolaos Kavvadias
Research Scientist, Hardware developer, B.Sc, M.Sc, Ph.D.
http://www.nkavvadias.com